Heretofore, for a tire condition detecting device configured to detect tire conditions such as inner pressure and temperature of a tire, the following structure has been widely adopted. Specifically, electronic components such as a transmitter and a pressure-temperature sensor are mounted on a circuit board which is housed in a casing (box unit) made from a synthetic resin.
For such a tire condition detecting device, a method is known in which the circuit board housed in the casing having an opening surface formed thereon is sealed with a sealant such as an epoxy based resin (for example, Patent Document 1). Sealing the circuit board housed in the casing with the sealant can suppress a breakdown of the tire condition detecting device, which would otherwise be caused by vibration or moisture.
The tire condition detecting device thus highly water-proofed is widely employed to a tire which is mounted on a dump truck used in mining mountains. This is because the tire has a coolant injected therein to suppress increase in temperature by running.